Gear differentials include compound planetary gear sets carried within a differential housing interconnecting a pair of output shafts for opposite directions of rotation with respect to the housing. An input shaft is connected to the housing for rotating the housing about a common axis of the output shafts. Sun gear members of the respective planetary gear sets, also referred to as "side" gears, are coupled to inner ends of the output shafts. Planet gear members of the planetary gear sets, also referred to as "element" gears, operatively connect the two side gears for relative rotation in a mutual driving relationship.
One known arrangement of the planetary gearing positions the side and element gears within the housing for rotation about axes that extend parallel to each other. Differentials with this type of gearing arrangement are referred to as "parallel-axis" gear differentials. The element gears of this type of differential are generally mounted in pairs within the differential housing. Preferably, the element and side gears are provided with helical teeth; and one portion of each element gear meshes with one of the side gears, while another portion of each element gear meshes with its paired element gear.
The invention herein relates to known designs of parallel-axis differentials in which the element gears are individually supported for rotation within pockets formed in the housings. The element-gear pockets have a predetermined shape with (a) an interior portion for mating with and providing bearings for slidably supporting the outside cylindrical surfaces of the element gears; (b) an opening providing clearance for the meshing engagement of each respective element gear with its respective side gear; and (c) an apron portion, adjacent the opening, demarcating the outer extremity of the bearing surface necessary to support the element gears so that their position remains appropriately fixed under outward thrust conditions. While such pocket designs have many important advantages, the relatively tight tolerances between the element-gear pockets and the outer cylindrical surfaces of the element gears make lubrication of these mating surfaces quite difficult.